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Cellular and Molecular Biology > Final: Ch 17 Myosin > Flashcards

Final: Ch 17 Myosin Flashcards

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1
Q

what are myosins

A

actin-based motor proteins that move along actin filaments

convert energy from ATP hydrolysis into movement along actin

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2
Q

myosin II

A

found in skeletal muscle

hundreds of molecules assemble into bundles

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3
Q

myosin V

A

binds vesicular cargo to transport it along actin filaments

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4
Q

domains of myosins

A

head

neck

tail

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5
Q

how to dissolve a myosin thick filament

A

solution of ATP and high salt

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6
Q

myosin II domains

A

2 heads and long tail connected by a flexible neck

tails intertwine and heads close together

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7
Q

myosin II has what type of activity

A

ATP hydrolysis (ATPase) in the S1 fragment

S1 also has F-actin binding site

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8
Q

all myosins have ___-_______ ATPase activity

A

actin-activated ATPase activity

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9
Q

sliding-filament assay

A

myosin attached to glass slide

actin filaments stained with phalloidin and ATP added

myosin heads walk toward + end, so looks like - end movement leads

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10
Q

tail domain

A

tailored to bind specific cargo

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11
Q

which domains of myosins are responsible for motor activity

A

head and neck (S1)

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12
Q

all myosin head domains convert what

A

ATP hydrolysis into mechanical work

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13
Q

myosin II assembles into _____ filaments

A

bipolar filaments

opposite orientations in each half so theres a cluster of head domains at each end

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14
Q

does myosin II have a short or long neck

A

short

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15
Q

myosin I

A

single headed

many functions

ex. connect actin filaments to membranes, endocytosis

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16
Q

myosin V domains

A

two heads and a long neck

tails dimerize

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17
Q

the length of the neck region affects the rate of myosin __________

A

movement

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18
Q

myosins move toward which end of the actin filament, except 1 myosin which moves toward the other end

A

+ end

myosin VI moves toward the - end

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19
Q

membrane-associated actin has their + end toward what?

A

the membrane

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20
Q

function of multinucleated skeletal muscle

A

produce gene products all along the cell

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21
Q

myosin heads do what along actin filaments

A

slide/”walk”

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22
Q

the hydrolysis of a single ATP molecule is coupled to each _____ taken by a myosin molecule along an actin filament

A

step

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23
Q

process of ATP-driven myosin movement along actin filaments

A

without ATP, the head is attached to F-actin

ATP binds the head, which releases the filament and hydrolyzes ATP –> ADP + Pi causing rocking

the myosin head binds actin

release of Pi is coupled to moving the actin filament forward (left) “power stroke”

ADP is released

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24
Q

the neck acts as a _____ point

A

pivot point

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25
Q

the myosin step size is proportional to what

A

neck length

tested by manipulating the genes for neck length (altered step size) and optical trap

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26
Q

step length of myosin II compared to myosin V

A

myosin V step length is 10x longer b/c of a very long neck (like a tether)

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27
Q

optical trap of myosin II

A

myosin on beads interacts with an actin filament held between 2 optical traps

when ATP is added, the myosin pulls the actin and a computer records the distance

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28
Q

what did the optical trap of myosin II show

A

that myosin II binds, moves, and releases the actin

it doesn’t bind continuously

29
Q

processive movement

A

myosin V takes sequential steps without releasing from actin

one head is always in contact with the actin

30
Q

does myosin V walk hand over hand on an actin filament?

A

yes

31
Q

can myosin V transport organelles?

A

yes

32
Q

do microtubules have classes that move in opposite directions?

A

yes

33
Q

what do the tail regions of myosins determine

A

what kind of cargo it carries

34
Q

myosin ____ filaments and actin _____ filaments in skeletal muscle slide past one another during _______

A

myosin thick, actin thin, contraction

35
Q

skeletal muscle fiber properties

A

long and multinucleated

striated

sarcomeres

36
Q

smooth muscle fiber properties

A

no sarcomeres

mononucleate

non-striated

37
Q

sarcomere

A

arrangement of actin/myosin

shortens by 70% during contraction

38
Q

thick filaments are composed of what

A

myosin II bipolar filaments

move toward Z disk where + ends are, causing contraction of the muscle

39
Q

skeletal muscle is structured by ________ and ________ proteins

A

stabilizing, scaffolding

actin capped by CapZ on the + end, and tropomodulin on the - end

nebulin goes from Z disk to tropomodulin (where it binds)

tintin is elastic and prevents overstretching

40
Q

skeletal muscle contraction is initiated by an increase in cytosolic __

A

Ca2+

41
Q

in skeletal muscle, a low cytosolic Ca2+ level is maintained by…

A

an ATPase that pumps Ca from the cytosol and into the sarcoplasmic reticulum

42
Q

an action potential opens what in skeletal muscle

A

voltage-gated Ca channels in the SR membrane to raise cytosolic Ca concentration and induce muscle contraction

43
Q

what effect does Ca have on skeletal muscle (thin-filament regulation)

A

changes tropomyosin and troponin which normally block myosin binding

allows myosin-actin interactions and therefore contraction

44
Q

contractile bundle

A

bundles composed of actin and myosin that are found in nonmuscle cells

less organized than skeletal muscle fibers

45
Q

in epithelial cells, contractile bundles are found as an ______ _____

A

adherens belt

46
Q

3 types of contractile bundle

A

adherens belt - epithelium

stress fibers -ECM

contractile ring - cell division

47
Q

skeletal muscle contraction is regulated by the ________-_______ complex bound to thin actin filaments

A

tropomyosin-troponin complex

switches between contraction inducing state in the presence of Ca, and the relaxed state without Ca

48
Q

how is smooth muscle contraction regulated

A

cycling of myosin II in response to extracellular signaling molecules

phosphorylation/dephosphorylation of myosin regulatory light chain by myosin LC kinase (thick-filament regulation)

49
Q

myosin V bound vesicles are carried along _____ filaments

A

actin

50
Q

myosin V in budding yeast

A

carries secretory vesicles along actin filaments into the bud

distributes organelles

51
Q

myosin V in giant green algae

A

cytoplasmic streaming

myosin V carries ER, which also moves cytoplasm

52
Q

cell migration results from what

A

coordinated motions generated in different parts of the cell integrated with an endocytic cycle

53
Q

how is cell migration initiated

A

formation of a large membrane protrustion at the leading edge of the cell - lamellipodium

54
Q

cell migration of a fibroblast

A

membrane extension occurs at the leading edge where the network of actin filaments is nucleated by Arp2/3 (forms lamellipodium)

some lamellipodia anchor to the substratum via focal adhesions

the cell body is translocated forward by myosin II cortical contraction at rear of cell

focal adhesions at the back of the cell are broken and integrins recycled by endocytosis

freed tail snaps forward

55
Q

the cell-adhesion molecules that mediate most cell-matrix interactions are membrane proteins called ______

A

integrins

external domain binds ECM (fibronectin and collagen)

cytosolic domain links them to the actin cytoskeleton

56
Q

2 importances of focal adhesion attachment

A

prevents leading lamella from retracting

attaches cell to the substratum, allowing for forward movement

57
Q

what 3 small GTP-binding proteins control actin organization

A

Rho

Rac

Cdc42

58
Q

what do growth factors like epidermal growth factor and platelet-derived growth factor do

A

bind cell surface receptors and stimulate cells to move and then divide

ex. in a wound, platelets become active and secrete PDGF to attract fibroplasts and epithelial cells to the wound

59
Q

what effect does dominant negative Rac have on wound healing

A

wound fails to close b/c Rac is needed to activate the Arp2/3 complex to form a lamellipodium

60
Q

Cdc42 is critical for regulating ________ of cells

A

polarity

dominant negative results in formation of leading edge, but movement in random directions

61
Q

migrating cells are steered by _______ molecules

A

chemotactic

ex. WBC are guided toward an infection by a tripeptide secreted by bacterial cells

62
Q

common mechanism of chemotaxis

A

binding cell surface receptors

activate intracellular signaling pathways

remodel cytoskeleton through activation or inhibition of actin binding proteins

63
Q

chemotaxis and amoebas

A

when stressed, these amoebas secrete cAMP which causes them to move toward each other

they them form a slug and make starvation-resistant spores

64
Q

membrane recycling in cell migration

A

membrane needed to form lamellipodia is provided from internalization of adhesion molecules (including integrins) from old focal attachments to front of cell

65
Q

dominant active protein

A

mutant small GTPase locked in the active state

66
Q

dominant active Cdc42

A

appearance of filopodia through Arp2/3 activation via the NPF WASp

67
Q

dominant active Rac

A

membrane ruffles/lamellipodium

68
Q

dominant-active Rho

A

stress fibers that contract

69
Q

general model of how cell migration is controlled via Rac, Rho, Cdc42

A

Cdc42 orients cell

oriented cell has high Rac activity in front to form lamellipodium

Rho activity is high in the rear to assemble contractile structures and activate myosin II

Cellular and Molecular Biology (34 decks)

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